"That depends son, if the potion is one of the Dark Arts or not. Typically, they are used to bolster a shielding or warding spell. But the Dark Arts... they can tap into the poisonous traits of the King of Snakes, and use it as a weapon."

Crookshanks by now has gotten into the den of the basilik, and found one of his scales that was shed by natural process. He picks it up in his mouth. Then heads back to find Jim.